Method of selecting inks for use in imaging with an imaging apparatus

ABSTRACT

A method of selecting inks for use in imaging with an imaging apparatus includes determining a maximum usage of a diluted ink for use in conjunction with a saturated ink based on visual perception characteristics relating to a combination of the diluted ink and the saturated ink; generating an initial colorant space based on the maximum usage of the diluted ink, the initial colorant space expressing an initial usage of the diluted ink and an initial usage of the saturated ink at each point in the initial colorant space; optimizing the initial usage of the diluted ink and the initial usage of the saturated ink in the initial colorant space to generate a final usage of the diluted ink and a final usage of the saturated ink in a final colorant space; and generating a color conversion lookup table based on the final colorant space.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to printing, and, more particularly, to amethod of selecting inks for use in imaging with an imaging apparatus.

2. Description of the Related Art

In recent years many inkjet printers with multilevel color inks,sometimes referred to as “photo printers,” have been developed for homeand office use. These printers typically perform six-color printing, andemploy saturated cyan, saturated magenta, saturated yellow, saturatedblack, diluted cyan, and diluted magenta inks (CMYKcm). The photoprinter cartridges are generally organized in such a way that thesaturated cyan, magenta, and yellow inks are in one cartridge, referredto as a “color cartridge,” and the diluted cyan, diluted magenta, andsaturated black are in another cartridge, referred to as a “photocartridge.” The use of diluted inks helps to improve image quality so asto achieve photo-quality images. However, visual artifacts, such asmottling and smearing, are created if the diluted inks are not usedappropriately.

The inks in the color and photo cartridges are typically eitherdye-based or pigment-based inks. The dye-based inks have a larger colorgamut than pigment-based inks, but poorer light fastness, especially forthe diluted inks, whereas the pigment-based inks have a smaller colorgamut but much better light fastness. Light fastness pertains to theability of a printed image to retain its original colorfulness, withoutexcessive fading over a period of time. In order to provide a largecolor gamut while providing good light fastness, a hybrid approach hasbeen taken, wherein both dye-based inks and pigment-based inks areemployed by the photo printer to render images. Another advantage ofusing the hybrid approach is that it has good dynamic range of lightnessacross the range of different types of print media.

However, a problem with the hybrid approach is that the gloss transitionbetween the pigment-based inks and the dye-based inks on glossy paperresults in serious visual artifacts. Thus, in order to improve imagequality by using the hybrid approach, not only must problems associatedwith using diluted and saturated inks be resolved, but the problemsassociated with using both dye-based inks and pigment-based inks mustalso be resolved so that both diluted and saturated inks in the form ofdye-based inks and pigment-based inks may be employed by the photoprinter.

What is needed in the art is an improved method of selecting inks foruse in imaging with an imaging apparatus.

SUMMARY OF THE INVENTION

The present invention provides an improved method of selecting inks foruse in imaging with an imaging apparatus.

The invention, in one form thereof, relates to a method of selectinginks for use in imaging with an imaging apparatus. The method includesdetermining a maximum usage of a diluted ink for use in conjunction witha saturated ink based on visual perception characteristics relating to acombination of the diluted ink and the saturated ink; generating aninitial colorant space based on the maximum usage of the diluted ink,the initial colorant space expressing an initial usage of the dilutedink and an initial usage of the saturated ink at each point in theinitial colorant space; optimizing the initial usage of the diluted inkand the initial usage of the saturated ink in the initial colorant spaceto generate a final usage of the diluted ink and a final usage of thesaturated ink in a final colorant space; and generating a colorconversion lookup table based on the final colorant space.

The invention, in another form thereof, relates to a method of selectinginks for use in imaging with an imaging apparatus. The method includesprinting a plurality of color patches on a substrate using a diluted inkand a saturated ink; determining at least two of granularity, gloss, anda substrate ink tolerance, based on the plurality of color patches;determining a maximum usage of the diluted ink for use in conjunctionwith the saturated ink based on visual perception characteristicsrelating to a combination of the diluted ink and the saturated ink,wherein the visual perception characteristics are based on the at leasttwo of the granularity, the gloss, and the substrate ink tolerance;generating an initial colorant space based on the maximum usage of thediluted ink, the initial colorant space expressing an initial usage ofthe diluted ink and an initial usage of the saturated ink at each pointin the initial colorant space; and generating a color conversion lookuptable based in part on the initial colorant space.

The invention, in yet another form thereof, relates to a method ofselecting inks for use in imaging with an imaging apparatus. The methodincludes generating an initial colorant space, the initial colorantspace expressing an initial usage of the diluted ink and an initialusage of the saturated ink at each point in the initial colorant space;optimizing the initial usage of the diluted ink and the initial usage ofthe saturated ink in the initial colorant space to generate a finalusage of the diluted ink and a final usage of the saturated ink in afinal colorant space; and generating a color conversion lookup tablebased on the final colorant space.

An advantage of the present invention is reducing mottling and smearingin an image.

Another advantage is that paper-cockling and soak-through of theprinting substrate may be avoided.

Yet another advantage is the reduction of glossy transition artifactsand increased smoothness of color transitions, while retaining theadvantages of the hybrid approach of using dye-based and pigment-basedinks, such as large color gamut, improved light fastness, and gooddynamic range of lightness across a range of different print media.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention,and the manner of attaining them, will become more apparent and theinvention will be better understood by reference to the followingdescription of embodiments of the invention taken in conjunction withthe accompanying drawings, wherein:

FIG. 1 is a diagrammatic depiction of an imaging system that employs animaging apparatus in accordance with the present invention.

FIG. 2 is a diagrammatic depiction of a colorspace converter accessing acolor conversion lookup table in accordance with the embodiment of FIG.1.

FIG. 3 is a flowchart that generally depicts an embodiment of a methodin accordance with the present invention.

FIG. 4 is a flowchart that depicts a method of determining a maximumusage of diluted ink (MUDI) in accordance with the embodiment of FIG. 3.

FIG. 5 is a plot depicting a gloss difference (color patch gloss minussubstrate gloss) characteristic of diluted cyan ink.

FIG. 6 is a flowchart that depicts a method of generating an initialcolorant space based on a maximum usage of diluted ink in accordancewith the embodiment of FIG. 3.

FIG. 7 is a plot depicting the change of lightness (L*) with actualdigital count for cyan.

FIG. 8 is a plot depicting a target color profile for cyan.

FIG. 9 is a plot depicting a cyan mixing table.

FIG. 10 is a plot depicting a magenta mixing table.

FIG. 11 is a plot depicting a yellow mixing table.

FIG. 12 is a flowchart that depicts a method of optimizing the usage ofdiluted and saturated inks in accordance with the embodiment of FIG. 3.

FIGS. 13A and 13B are an image and a corresponding lightness/darknessscale used in illustrating a reduction of usage of diluted ink inaccordance with the embodiment of FIG. 3.

FIG. 14 is a flowchart that depicts a method of generating a colorconversion lookup table in accordance with the embodiment of FIG. 3.

Corresponding reference characters indicate corresponding partsthroughout the several views. The exemplifications set out hereinillustrate embodiments of the invention, and such exemplifications arenot to be construed as limiting the scope of the invention in anymanner.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, and particularly to FIG. 1, there isshown a diagrammatic depiction of an imaging system 10 embodying thepresent invention. Imaging system 10 includes an imaging apparatus 12and a host 14. Imaging apparatus 12 communicates with host 14 via acommunications link 16.

Imaging apparatus 12 may be, for example, an ink jet printer and/orcopier, or an all-in-one (AIO) unit that includes an inkjet printer, ascanner, and possibly a fax unit. In the present embodiment, imagingapparatus 12 includes a controller 18, a print engine 20, a colorprinting cartridge 22, a photo printing cartridge 24, and a userinterface 26.

Controller 18 includes a processor unit and associated memory 36, andmay be formed as one or more Application Specific Integrated Circuits(ASIC). Controller 18 is a printer controller, but may alternatively bea scanner controller, or combined printer and scanner controller.Although controller 18 is depicted in imaging apparatus 12,alternatively, it is contemplated that all or a portion of controller 18may reside in host 14. Controller 18 is communicatively coupled to printengine 20 via a communications link 38, and to user interface 26 via acommunications link 42. Controller 18 serves to process print data andto operate print engine 20 to perform printing.

Print engine 20 is configured to mount one or more of color printingcartridge 22 and one or more of photo printing cartridge 24 and to printon a substrate 44 using color printing cartridge 22 and photo printingcartridge 24. Print engine 20 is capable of printing with multilevelhybrid inks including a diluted ink and a saturated ink, wherein thediluted ink is one of a pigment-based ink and a dye-based ink, and thesaturated ink is the other of the pigment-based ink and the dye-basedink. As set forth below, in the present embodiment, the saturated inksemployed by imaging apparatus 12 are dye-based, and the diluted inks arepigment-based. Alternatively, however, it is contemplated that eachsaturated ink and diluted ink may be dye-based or pigment based, whereinsome saturated inks are dye-based, while others are pigment-based, andwherein some diluted inks are pigment based, while others are dye-based.

Color printing cartridge 22 is capable of printing various colors ofink, such as saturated cyan (C), saturated magenta (M), and saturatedyellow (Y) dye-based inks. The term, “saturated” refers to the fact thatthe inks are full-strength such as the inks used by conventional CMYKink jet printers, and are not, for example, diluted inks. Color printingcartridge 22 is also capable of printing at least two drop sizes, ordrop masses, of ink, including a large drop mass and a small drop mass.

Photo printing cartridge 24 is capable of printing saturated black (K),diluted cyan (c), and diluted magenta (m) inks, as well as printing atleast two drop sizes, or drop masses, of ink, including a large dropmass and a small drop mass. The diluted cyan and diluted magenta inksprinted by photo printing cartridge 24 are pigment based, and the blackink printed by photo printing cartridge 24 is also a pigment-based ink.

Imaging apparatus 12, as an ink jet printer, is configured to printusing CMY inks in color printing cartridge 22 and Kcm inks in photoprinting cartridge 24.

Accordingly, when printing using color printing cartridge 22 and photoprinting cartridge 24, print engine 20 performs six-color printing,wherein the six colors are cyan, magenta, yellow, black, diluted cyan,and diluted magenta (CMYKcm). The combination of dye-based inks andpigment-based inks is referred to as hybrid inks. In addition, the cyanand magenta inks may be referred to as multilevel inks, based on thefact that there are more than one “level” associated with each ink colorthat may be printed using print engine 20: saturated, diluted, as wellas levels associated with drop size/mass. Although reference is madeherein to saturated and diluted inks, it will be understood by thoseskilled in the art that the use of more than two different inkconcentrations may be employed without departing from the scope of thepresent invention.

Substrate 44 is a print medium, and may be one of many types of printmedia, such as a sheet of plain paper, fabric, photo paper, coated inkjet paper, greeting card stock, transparency stock for use with overheadprojectors, iron-on transfer material for use in transferring an imageto an article of clothing, and back-lit film for use in creatingadvertisement displays and the like. As an ink jet print engine, printengine 20 operates color printing cartridge 22 and photo printingcartridge 24 to eject ink droplets onto substrate 44 in order toreproduce text or images, etc.

Host 14 may be, for example, a personal computer, including memory 46,an input device 48, such as a keyboard, and a display monitor 50. Aperipheral device 52, such as a digital camera, is coupled to host 14via a communication link 54. Host 14 further includes a processor,input/output (I/O) interfaces, memory, such as RAM, ROM, NVRAM, and atleast one mass data storage device, such as a hard drive, a CD-ROMand/or a DVD unit.

During operation, host 14 includes in its memory a software programincluding program instructions that function as an imaging driver 58,e.g., printer/scanner driver software, for imaging apparatus 12. Imagingdriver 58 is in communication with controller 18 of imaging apparatus 12via communications link 16. Imaging driver 58 facilitates communicationbetween imaging apparatus 12 and host 14, and may provide formattedprint data to imaging apparatus 12, and more particularly, to printengine 20. Although imaging driver 58 is disclosed as residing in memory46 of host 14, it is contemplated that, alternatively, all or a portionof imaging driver 58 may be located in controller 18 of imagingapparatus 12, for example, in memory 36 or a firmware component ofcontroller 18.

Referring now to FIG. 2, imaging driver 58 includes a colorspaceconverter 60. Although described herein as residing in imaging driver58, colorspace converter 60 may be in the form of firmware or software,and may reside in either imaging driver 58 or controller 18.Alternatively, some portions of colorspace converter 60 may reside inimaging driver 58, while other portions reside in controller 18.

Coupled to colorspace converter 60 is a color conversion lookup table62. Colorspace converter 60 converts color signals from an RGBcolorspace output by display monitor 50 to an output colorspace usingcolor conversion lookup table 62. For example, the output colorspace maybe CMYKcm. Color conversion lookup table 62 is a multidimensional lookuptable having at least three dimensions, and includes RGB input valuesand the corresponding CMYKcm output values. Color conversion lookuptable 62 may also include other data, such as spectral data.

Color conversion lookup table 62 may be in the form of groups ofpolynomial functions capable of providing the same multidimensionaloutput as if in the form of a lookup table. As shown in FIG. 2, forexample, colorspace converter 60 converts input RBG color data intoCMYKcm output data, using color conversion lookup table 62.

Referring now to FIG. 3, a method of selecting inks for use in imagingwith imaging apparatus 12 is depicted.

At step S100, a maximum usage of diluted ink (MUDI), e.g., for dilutedcyan ink and for diluted magenta ink, for use in conjunction withsaturated ink, e.g., cyan, magenta, and/or yellow saturated inks, isdetermined based on visual perception characteristics relating to acombination of diluted ink and said saturated ink. Visual perceptioncharacteristics may include, for example, lightness, granularity, gloss,and substrate ink tolerance. Step S100 is described in greater detailbelow with respect to FIGS. 4 and 5, and steps S100-1 to S100-7.

At step S102, an initial colorant space is generated based on themaximum usage of diluted ink. As will be appreciated by those skilled inthe art, a colorant space includes many colorant points, each of whichexpresses a value pertaining to a quantity of ink for each color of inkaccounted for in the colorant space, for example, 8-bit color values inthe range of 0 to 255 for each of cyan, magenta, yellow, black, dilutedcyan, and diluted magenta. The initial colorant space expresses aninitial usage of the diluted ink and an initial usage of the saturatedink at each point in the initial colorant space. Step S102 is describedin greater detail below with respect to FIGS. 6-11, and steps S102-1 toS102-9.

At step S104, the initial usage of diluted ink and the initial usage ofsaturated ink in the initial colorant space is optimized to generate afinal usage of diluted ink and a final usage of saturated ink in a finalcolorant space. Step S104 is described in greater detail below withrespect to FIGS. 12, 13A, and 13B, and steps S104-1 to S104-7.

At step S106, color conversion lookup table 62 is generated based on thefinal colorant space. Step S106 is described in greater detail belowwith respect to FIG. 14 and steps S106-1 to S106-11.

Referring now to FIG. 4, the determination of the MUDI based on visualperception characteristics, as set forth in step S100 of FIG. 3, isdescribed in greater detail below with respect to steps S100-1 toS100-7.

The objective of multilevel ink printing is to achieve photographicquality by reducing the image graininess. Within a certain range from alight to a dark image area, the use of diluted ink may be used to reducethe image graininess. However, as set forth above, the diluted cyan andmagenta inks are pigment-based inks, whereas the saturated cyan,magenta, and yellow inks are dye-based inks. Too much diluted ink mayresult in visual artifacts, such as an unacceptable glossy transitionfrom the diluted pigment-based inks to the saturated dye inks at certaindarker portions of the image, i.e., darker image areas. This is causedby the difference in gloss between printing with pigment-based inks anddye-based inks.

In addition, without regard to the effect on gloss by using differentinks, too much use of the diluted inks may result in too much water onthe paper, which leads to other serious visual artifacts, such asmottling of the image, smearing of the ink, and the soaking of inkthrough substrate 44, which is referred to as soak-thru. In addition,paper-cockling may occur in substrate 44. Such artifacts are related tothe use of multilevel inks, and to the amount of ink that can betolerated by substrate 44. For example, inherent in the use ofmultilevel inks is that the amount of water ejected onto the paperincreases beyond that of single level inks due to the use of dilutedinks. Many substrates cannot quickly or completely absorb all the ink,resulting in the aforementioned visual artifacts. Some substrates may beable to absorb higher amounts of ink during low-speed printing, e.g.,wherein there is enough time to absorb the ink, but when used in higherspeed printing, mottling occurs due to the inability to quickly absorball of the different colors of ink being ejected onto the substrate.

In order to reduce the likelihood of such visual artifacts, whilemaintaining the advantage of dilute inks in reducing image graininess,and while allowing higher speed printing, measurements of lightness,granularity, and gloss, and substrate ink tolerance are recommended,wherein the amount of usage of diluted inks to be used in printing isdetermined based on these measurements.

At step S100-1, a plurality of color patches is printed on substrate 44using the cyan and magenta diluted inks, and using the cyan, magenta,and yellow saturated inks. The color patches are selected as follows.

For each level of ink (e.g., diluted or saturated), n evenly spacedpoints covering the whole digital range, e.g., 0 to 255 for eight bitcolor, are selected. For multilevel ink (e.g. cyan or magenta), allcombinations of the n-point diluted and n-point saturated inks are usedto print n×n patches. For single level ink (e.g. yellow), n points areused to print n patches. Acceptable results were obtained by theinventors using n=9.

At step S100-3, lightness, granularity, gloss, and a substrate inktolerance are determined based on the plurality of color patches. Thevisual perception characteristics of step S100 are determined based onat least one of granularity, gloss, and substrate ink tolerance. In apreferred embodiment, the visual perception characteristics are based oneach of granularity, gloss, and substrate ink tolerance. For example,granularity, gloss, and substrate ink tolerance are measured for eachprinted patch. In addition, the lightness (L* in the CIELAB colorspacesystem) of each patch is measured using a spectrophotometer.

The granularity may be measured with a granularity meter. If agranularity meter is not available, a visual examination score for thegranularity (0-100, with 100 being the most granularity) is given toeach of the patches.

The gloss at 60 degrees is measured with a gloss meter.

The substrate ink tolerance is determined by examining the printedpatches. For example, if ink soak-thru is observed, the substrate inktolerance has been exceeded. Knowing the amount of ink that was used togenerate each color patch, for example, based on the digital countsinput into print engine 20 by controller 18 for printing the colorpatches, allows a determination of how much ink resulted in soak throughof substrate 44, and hence, allows a determination of substrate inktolerance.

At step S100-5, the maximum usage of diluted ink (MUDI) is determinedfor each visual perception characteristic, e.g., granularity, gloss, andsubstrate ink tolerance.

The theoretical upper limit of the maximum usage of diluted ink is 100%diluted ink (digital count=255 for 8-bit data). However, in practice,the maximum usage of diluted ink at any given color point may be lessthan 100% so that visual perception characteristics, e.g., thegranularity improvement limit, gloss difference and gloss transitionfrom diluted pigment ink to saturated dye ink, or mottling, smearing,and soak-through that are associated with the substrate ink tolerance,will be within acceptable limits.

The MUDI based on the granularity improvement limit is the minimumdiluted ink usage at which increasing usage of diluted ink will notsignificantly improve the granularity. This can be determined byexamining the granularity values from light to dark patches.

Referring now to FIG. 5, the MUDI based on gloss is determined by glossmeasurements. FIG. 5 illustrates the gloss difference values (colorpatch gloss minus substrate gloss) changing with the diluted ink usagefor diluted cyan ink. It can be seen that the gloss difference valueincreases with the usage of the diluted ink. The acceptable glossdifference value is determined by visual examination of the printedpatches and/or experience. One way to gain the experience is thatseveral gloss difference values are first chosen based on the printedpatches, then for each selected gloss difference value (corresponding toa MUDI) the remaining process is completed and a color reproductiontable is built to print representative images, with emphasis on thetransition from diluted pigment ink to saturated dye ink within theimage. Finally an acceptable gloss difference value, and hence acorresponding MUDI, is determined based on the comparison of the printedimages.

The MUDI based on substrate ink tolerance is determined by examining theprinted patches. The maximum diluted ink should be decreased if smearingor show-through (soak-thru) occurs due to an excessive amount of dilutedink.

Referring again to FIG. 4, at step S100-7, the lowest maximum usage ofdiluted ink is selected from the group of MUDI's individually determinedin step S100-5 based on each of granularity, gloss, and substrate inktolerance, for example, the lowest of the MUDI's calculated for each ofgranularity, gloss, and substrate ink tolerance.

Referring now to FIG. 6, the generation of the initial colorant spacebased on the maximum usage of diluted ink, as set forth in step S102 ofFIG. 3, is described in greater detail below with respect to stepsS102-1 to S102-9.

The general rule for multilevel ink mixing is that the diluted ink isused primarily to reproduce light colors and the saturated ink is usedprimarily to reproduce dark colors. Both the diluted and saturated inksmay be used for middle-tone colors. Mixing tables, also referred toherein as 1-D lookup tables, are generated to determine both the initialusage of the diluted ink and the initial usage of the saturated inkbased on the maximum usage of the diluted ink, as set forth below. Theinitial colorant space is generated based on the initial usage ofdiluted ink and the initial usage of saturated ink. The term, “mixing,”as employed herein, does not refer to a physical mixing of differentinks, e.g., diluted and saturated inks, as would yield a mixture ofthose inks into, for example, a common reservoir, but rather, refers toselecting an amount of each ink for placement on substrate 44 at a givenpixel in order to reproduce the desired color.

The initial usage of the diluted ink and the initial usage of thesaturated ink refer to the amounts of the diluted ink and the saturatedink, respectively, that are expressed by a digital count in the initialcolorant space for each point in that colorant space. For example, acolorant point (120, 125, 130, 60, 25, 30) in a CMYKcm initial colorantspace represents a particular color point having a digital count (basedon the input tone) for saturated cyan of 120, and digital counts forsaturated magenta, saturated yellow, black, diluted cyan, and dilutedmagenta of 125, 130, 60, 25, and 30, respectively, that would otherwisebe input to a halftoner (not shown) for possible printing of a pixel. Inthe present embodiment, however, colorant points from the initialcolorant space may not be printed directly; rather, as set forth abovein step S104 of FIG. 3, the usage of diluted and saturated inks isoptimized to generate a final usage of diluted ink and a final usage ofsaturated ink in a final colorant space, which is then used to createcolor conversion lookup table 62 for printing. Hence, it is the digitalcounts of the final colorant space that are input to the halftoner forprinting.

At step S102-1, target color profiles are determined for each primarycolor ink, e.g., cyan, magenta, and yellow.

Referring now to FIG. 7, the change of lightness (L*) with the actualdigital count (C₀) of cyan is depicted. The actual digital countgenerally represents the value sent to imaging apparatus 12 for printinga particular ink at a particular pixel. The paper white is at digitalcount=0, and the solid color (darkest cyan color) is at digitalcount=255 (maximum value for 8-bit representation). It is shown in FIG.7 that the change of lightness with the actual digital count isnon-linear. Since a more linearized color space would result in lessinterpolation errors in later processing, a digital count lookup table,wherein the table index (abscissa) is a nominal digital count (x₀) andthe table content (ordinate) is the actual digital count (C₀), isconstructed in such a way that when the nominal digital count changesfrom 0 to 255, the actual digital count (C₀) changes non-linearly from 0to 255, whereas the lightness (L*) changes linearly from the white pointto the darkest point.

Referring now to FIG. 8, a linearized lightness profile is defined withrespect to the nominal digital count (x₀) as the “target color profile.”To determine the target color profile, only the lightness (L*) of paper(substrate 44) white and that of the darkest (solid) color as printed onsubstrate 44 are required.

For the target color profile of multilevel ink, it is necessary to knowwhich levels of the ink can be printed on the darkest color. This mayvary from one printing system to another. The general rule is that thediluted ink will not be printed at the darkest color and only saturatedink will be printed at the darkest color.

Referring now to FIGS. 6 and 9, at step S102-3, initial usage of thediluted ink is determined.

The objective of mixing different printing levels is, for a given targetcolor profile index (nominal digital count x_(0i)), to find anappropriate combination of the levels (e.g., diluted and saturatedlevels) to produce the desired lightness (L*) at the index. For example,with reference to FIG. 9, the following procedures are used in thepresent embodiment to determine the initial usage of diluted ink, afterwhich, the initial usage of the saturated ink is determined.

-   -   (a) Initially, set all mixing tables to zeros.    -   (b) Select the diluted ink, which represents a level of        multilevel ink, and start from the white point (index=0) in the        target color profile.    -   (c) Increase the target color profile index by 1 and find the        target L*.    -   (d) Change only the currently-selected level's actual digital        count and keep the other levels' actual digital counts        unchanged. Use an interpolation scheme and all levels' actual        digital counts at the current target index to compute the        lightness value until matching the target L*. Put the matched        actual digital count in the current level's lookup table.    -   (e) Continue steps (c) and (d) until the matched actual digital        count reaches the maximum usage of diluted ink (MUDI) determined        at step S100 of FIG. 3. The plotted data left of the vertical        line in FIG. 9 is the mixing result obtained so far for the        diluted ink. Record the current target profile index        (corresponding to the peak) as the peak index (P in FIG. 9).    -   (f) Flip (mirror) the plotted data to the right side of the        vertical line at the peak index P. If the flipped part is beyond        the maximum index (255), it may be linearly scaled to the        maximum index. This completes the process of mixing the diluted        ink.

At step S102-5, initial usage of saturated ink is determined.

-   -   (a) Select the saturated ink and start from the last peak index        P in the target color profile obtained above (for a single-level        ink like yellow, the last peak index will be zero).    -   (b) Increase the target color profile index by 1 and find the        target L*.    -   (c) Change only the currently-selected level's actual digital        count and keep other levels' actual digital counts unchanged.        Use an interpolation scheme and all levels' actual digital        counts at the current target index to compute the lightness        value until matching the target L*. Put the matched actual        digital count in the current level's lookup table.    -   (d) Continue steps (b) and (c) until the matched actual digital        count reaching the maximum value (255). This completes the        process of mixing the saturated ink.

Referring again to FIG. 6, at step S102-7 a smoothing process isperformed on the mixing tables. Since the mixing tables are determinedbased on measurement data, noise in the measurement data is propagatedinto the mixing table. In the present embodiment, a running-averagescheme is employed to smooth the mixing tables. A run-length of 11points was found suitable for this purpose. That is, for each point inthe table of each printing level, the original point is replaced withthe average of the left 5 points, itself, and the right 5 points.

FIGS. 9-11 depict the smoothed mixing tables for cyan, magenta, andyellow, respectively.

At step S102-9, the initial colorant space is formed, based on initialusage of diluted ink and the initial usage of the saturated ink. Forexample, the above procedures (steps S102-1 to S102-7) have produced onedimensional (1-D) lookup tables along cyan, magenta, and yellow nominaldigital count axes. The three nominal axes will form a 3-D cubeincluding 16 million (256×256×256) color mixing points. At each mixingpoint, there exist 5 digital counts: C₀ (saturated cyan), M₀ (saturatedmagenta), Y₀ (saturated yellow), c₀ (diluted cyan), and m₀ (dilutedmagenta). This space is referred to as the initial colorant space. Thecyan, magenta, and yellow nominal digital count axes are denoted as x₀,x₁, x₂ respectively. A coordinate of a mixing point in this space isdenoted by (x₀, x₁, x₂) at which there exists 5 digital counts: (C₀, M₀,Y₀, c₀, m₀).

Referring now to FIG. 12, the optimization of the initial usage ofdiluted ink and the initial usage of saturated ink in the initialcolorant space to generate the final usage of diluted ink and the finalusage of saturated ink in the final colorant space, as set forth in stepS104 of FIG. 3, is described in greater detail below with respect tosteps S104-1 to S104-7.

The main purpose of using diluted inks is to minimize the graininess oflight and middle-tone color images. The darker color images should notuse diluted inks for two reasons: (1) no significant graininessimprovements can be achieved by using the diluted inks; and (2) too muchink on the paper (substrate 44) will cause smearing, soak-thru, andpaper cockles, resulting in a loss of aesthetic appeal of the printedimages. However, the initial colorant space contains subsets ofunnecessary diluted inks. For example, a color mixing point (255, 0,255, 0, 255) (100% saturated cyan mixed with 100% yellow and 100%diluted magenta) exists in the initial colorant space. Such a colorantpoint is not appropriate, because mixing 100% saturated cyan with 100%yellow results in a very saturated color, and further mixing with anydiluted ink not only yields no improvement in graininess, but alsoresults in too much water (from the ink) being ejected onto the paper.This problem may be solved by the following optimization procedures.

At step S1104-1, a primary diluted ink ratio is computed.

When generating the 1-D lookup tables (mixing tables), a preferredstrategy is how to determine how much diluted ink should be used at eachmixing point along the primary ink axis, since the diluted ink usagewill determine the image graininess and smoothness of color transition.The ratio of the diluted ink at each color mixing point along theprimary ink axis (x) is referred to as the Primary Diluted Ink Ratio,and is given by: $\begin{matrix}{{R_{i}(x)} = \frac{D_{i0}(x)}{{D_{i0}(x)} + {S_{i0}(x)}}} & \left( {{Equation}\quad 1} \right)\end{matrix}$where D_(i0)=digital count at x of the ith diluted ink beforemodification, i=0 for cyan and i=1 for magenta; S_(i0)=digital count atx of the ith saturated ink before modification; and R_(i)=ratio of theith diluted ink to the total of the ith saturated and ith diluted ink atx before modification.

At step S104-3, a new 3-D diluted ink ratio is determined so as tooptimize the initial usage of diluted ink in the initial colorant spaceto generate a final usage of diluted ink for use in the final colorantspace.

As set forth previously, the initial colorant space is constructed bythe 1-D lookup tables (mixing tables). Therefore, in the initialcolorant space, the diluted ink ratio of a colorant at any mixing pointwill be equal to the corresponding primary diluted ink ratio. Forexample, the diluted ink ratio of cyan at (x₀, x₁, x₂) will be equal tothe primary diluted ink ratio of cyan at (x₀, 0, 0). As mentioned above,the usage of diluted ink determined this way is too much for somesubsets in the 3-D initial colorant space. Accordingly, it is desirableto compute a new 3-D diluted ink ratio (F_(i)) such that the new dilutedink (D_(i)) at each color mixing point in the initial colorant space isgiven by $\begin{matrix}{D_{i} = {{F_{i}\left( {D_{i0} + S_{i0}} \right)}\quad{Or}}} & \left( {{Equation}\quad 2} \right) \\{F_{i} = \frac{D_{i}}{D_{i0} + S_{i0}}} & \left( {{Equation}\quad 3} \right)\end{matrix}$where D_(i0) and S_(i0) are the original diluted and saturated inkdigital counts of cyan or magenta at the mixing point.

It is reasonable to assume that the 3-D diluted ink ratio, F_(i),increases with the primary diluted ink ratio (R_(i)) of the mixingpoint, and that 3-D diluted ink ratio should be related to somevariable, V, which depends on all of the primary diluted ink ratioswithin the same color mixing point (e.g., R₀ for cyan, and R₁ formagenta). The 3-D diluted ink ratio, F_(i), is thus assumed to take thefollowing form:F _(i) =[V(R ₀ ,R ₁)R _(i)]^(λ)  (Equation 4)where λ is a constant. To determine the 3-D diluted ink ratio (F_(i))function, the following two considerations are made:

(1) According to the first consideration, inspecting the 1-D lookuptables D_(i)(x) and S_(i)(x) shows that as the color becomes darker (xincreases), the primary diluted ink ratio approaches zero. When thisdarker color (e.g., cyan at a larger x₀) is mixed with another lightercolor (e.g., magenta at smaller x₁), the lighter color should not usemuch diluted ink since the mixed color is already “dark”. Accordingly,letξ=max(x ₀ ,x ₁ , . . . ,x _(n-1))  (Equation 5)where n is the number of primary colors that have diluted levels at amixing point, n=2 for a mixing point with two inks (e.g., cyan andmagenta) which both have diluted levels; and n=1 for any mixing point onthe cyan or magenta axis. Accordingly, based the present consideration,in conjunction with Equations 4 and 5, the variable, V, may bedetermined as a function of R₀ and R₁, as follows: $\begin{matrix}{{V\left( {R_{0},R_{1}} \right)} = {\frac{1}{n}{\sum\limits_{j = 0}^{n - 1}\quad{R_{j}(\xi)}}}} & \left( {{Equation}\quad 6} \right)\end{matrix}$

An example of R_(j)(x) is provided as follows: at x₀=200 (cyan index)and x₁=100 (magenta index), x will be 200, R₀(200) will be the primarydiluted cyan ratio at x=200, computed with Eq. 1, and R₁(200) will bethe primary diluted magenta ratio at x=200 (not x=100), computed withEquation 1. Selecting x according to Equation 5 will make the dilutedink ratio of the darkest colorant (after middle tone color, the darkercolor will have less diluted ink; see FIGS. 9 and 10) in the mixingpoint play an important role, leading to a smaller F_(i) (Equations. 4and 6), and hence less diluted ink (Equation 2) for the darker imagearea than that determined in step S102-3 for the initial colorant space.With the present example in mind, it is seen that the initial usage ofdiluted ink is reduced at particular points in the initial colorantspace in order to generate a final usage of diluted ink for use in thefinal colorant space.

(2) According to the second consideration, it is understood thatEquation 4 is a general function and should satisfy the followingboundary condition: On the primary cyan (or magenta) axis, the dilutedink determined in step S102-3 should not be modified. This means bycomparing Equations 1 and 3 that the new 3-D diluted ink ratio should beequal to the primary diluted ink ratio under conditions appropriate tothe second consideration (e.g., those points on the primary cyan andmagenta axes). Hence, on the primary cyan (or magenta) axis, based onEquations 4 and 6:R _(i) =[R _(i) R _(i)]^(λ)  (Equation 7)

Solving the above equation gives $\begin{matrix}{\lambda = \frac{1}{2}} & \left( {{Equation}\quad 8} \right)\end{matrix}$By combining Equations 4, 6, and 8, the new 3-D diluted ink ratio,F_(i), is given by: $\begin{matrix}{F_{i} = \sqrt{\frac{R_{i}}{n}{\sum\limits_{j = 0}^{n - 1}\quad{R_{j}(\xi)}}}} & \left( {{Equation}\quad 9} \right)\end{matrix}$

Equations 2 and 9 are applied to all mixing points in the initialcolorant space in order to determine the final usage of diluted ink,which will be used to form the final colorant space.

At step S104-5, the initial usage of saturated ink is modified, e.g.,optimized, to generate the final usage of saturated ink, based on thefinal usage of diluted ink.

After the diluted ink is reduced from D_(i0) to D_(i) (Equation 2), thesaturated ink in the color mixing point is modified to maintain theoriginal colorfulness. One rigorous way to do this is to determine thenew saturated inks by making the new L*a*b* equal to the originalvalues, which could be done by using a color mixing model. However, forcomputational efficiency, making the new L* approximately equal to theoriginal value by the following method has proved to be a reasonableapproximation. Let:

-   -   L*_(d)(D)=the diluted ink L* profile, where D is diluted ink        digital count (0-255);    -   L*_(s)(S)=the saturated ink L* profile, where S is saturated ink        digital count (0-255).    -   L*_(s-1)(L*s)=the inverted function of the saturated ink L*        profile, wherein the output is saturated ink digital count        (0-255).    -   L*d_(i0)=the L* value of diluted ink before modification when        D=D_(i0), where i=0 for cyan and i=1 for magenta;    -   L*_(di)=the L* value of diluted ink after modification when        D=D_(i);    -   L*_(si0)=the L* value of saturated ink before modification when        S=S_(i0);    -   L*_(si)=the L* value of saturated ink after modification when        S=S_(i).

Then, equalizing the L* change due to the diluted ink reduction to theL* change due to the saturated ink increase gives (note that the L*decreases with increasing digital count):L* _(si) =L* _(si0)−(L* _(di) −L* _(di0))  (Equation 10)

Inverting the 1-D function L*_(s)(S) gives the modified saturated ink(S_(i)):S _(i) =L* _(s) ⁻¹(L* _(si))  (Equation 11)

Using Equations 1, 2, 5, 9, 10, and 11, the digital counts of a colorthat has a diluted level in a color mixing point will be modified forthe entire initial colorant space, yielding a modified colorant space.

At step S104-7, the final colorant space is formed based on the finalusage of diluted ink and final usage of saturated ink.

After the initial colorant space is modified as set forth above, a blackink mixing technique, such as that described in U.S. Pat. No. 6,776,473B2, assigned Lexmark International, Inc. of Lexington, Ky., is used tomix the black ink (K) into the modified colorant space. Each colormixing point in the colorant space will now contain 6 digital counts:(C, M, Y, K, c, m). This colorant space is referred to as the finalcolorant space.

An example of generating a colorant point in the final colorant space inaccordance with the present embodiment follows.

(1) Input variables:

-   -   a. 1-D lookup tables: cyan: D₀(x₀), S₀(x₀); magenta: D₁(x₁),        S₁(x₁); yellow: S₂(x₂).    -   b. 1-D L* profiles: cyan: L*_(d0)(D₀), L*_(s0)(S₀); magenta:        L*_(d1)(D₁), L*_(s1)(S₁).    -   c. x₀=255, x₁=127, x₂=10.

(2) Find the color mixing point at (x₀, x₁, x₂) from the 1-D lookuptables: CMYcm: (255, 0, 5, 0, 200), i.e., S₀₀=255, S₁₀=0, S₂₀=5, D₀₀=0,D₁₀=200.

(3) Compute the primary diluted ink ratios: cyan: R₀(x₀)=0/(0+255)=0,magenta: R₁(x₁)=200/(200+0)=1.

(4) Find the maximum value of x_(i) for colors that have diluted levels:>=max(x₀, x₁)=max(255, 127)=255.

(5) Compute primary diluted ink ratios at x=>: since >=255 is 100%saturated ink point, all diluted inks are zero. Therefore, cyan:R₀(>)=0, magenta: R₁(>)=0.

(6) Compute new 3-D diluted ink ratios: from Equation 9, F₀=0 for cyan,and F₁=0 for magenta.

(7) Modify diluted inks: from Equation (2), D₀=0 for cyan, and D₁=0 formagenta.

(8) Find L* values for D_(i0), S_(i0), and D_(i): these values can befound from the 1-D L* profiles. Here the diluted cyan in the examplepoint is zero and no modification is necessary. Only L* values formagenta must be found, based on:

L*_(d10)=L*_(d1)(D₁₀)=L*_(d1)(200)=67.0

L*_(s10)=L*_(s1)(S₁₀)=L*_(s1)(0)=93.0

L*_(d1)=L*_(d1)(D₁)=L*_(d1)(0)=93.0

(9) Compute the L* values of new saturated inks (for magenta only, inthe present example):

From Equation (10):

L*_(s1)=L*_(s10)−(L*_(d1)−L*_(d10))=93.0−(93.0−67.0)=67.0

(10) Compute new saturated inks (for magenta only, in the presentexample): suppose L*_(s1)(75)=67.0, then from Equation 1, S₁=75;

The above example has modified the original point (255, 0, 5, 0, 200)into (255, 75, 5, 0, 0), giving an ink reduction of 27%.

From the above, it will be appreciated by those skilled in the art thatoptimizing the initial usage of the diluted ink and the initial usage ofthe saturated ink in the initial colorant space yields a reduction inusage of the diluted ink and an increase in usage of the saturated inkin the final colorant space as compared to the initial colorant space.As set forth below, it is the final colorant space that is incorporatedinto color conversion lookup table 62. The reduction in usage of thediluted ink and the increase in usage of the saturated ink occursexclusively at darker portions of an image printed by imaging apparatus12 using color conversion lookup table 62.

For example, when printing colors that use small amounts of diluted cyanand/or diluted magenta, e.g., digital counts less than 40, not very muchink is ejected onto substrate 44 to reproduce such relatively lightcolors, and hence, there is no need to reduce the amount of diluted ink,since at such low amounts of usage, visual artifacts are unlikely. Hencea lower limit is set, below which, the amount of diluted ink will not bereduced, whereas for colors that are darker than the limit, the amountof diluted ink usage in the initial colorant space will be reduced. Thelower limit may be set to any value above which a reduction in dilutedink is required in order to reduce visual artifacts, and may be madehigher or lower than 40, which is merely an exemplary value. Forexample, the lower limit may be set at the mid-tone level of 8-bitcolor, which is 128. In such a case, there would be no reduction inusage of diluted ink in lighter portions of the picture, e.g., thoseportions having digital counts of less than 128, but in the darkerportions of the image, e.g., those portions having digital countsgreater than or equal to 128, there would be a reduction in usage of thediluted ink.

The amount of reduction in usage of the diluted ink increases withincreasing darkness within an image printed by imaging apparatus 12using color conversion lookup table 62, and the amount of increase inusage of the saturated ink increases with the increasing darkness, asmay be appreciated by those skilled in the art based on theaforementioned discussion of the present embodiment.

For example, referring now to FIGS. 13A and 13B, an image 64 and acorresponding lightness/darkness scale 66, respectively, are depicted.Lightness/darkness scale 66 illustrates the range of lightness, L*, ofimage 64. Location pointer 68 in image 64, represented by a “star”,indicates a relatively light portion of image 64, as is visuallyapparent in FIG. 13A, and which is indicated in lightness/darkness scale66 of FIG. 13B by location pointer 70. Because this portion of the imageis relatively light, no reduction in usage of diluted ink is required.Location pointer 72 in FIG. 13A, on the other hand, is seen in a darkerportion of image 64 than is location pointer 68, as indicated bylocation pointer 74 on lightness/darkness scale 66 of FIG. 13B, where areduction in usage of diluted inks is likely warranted. Location pointer76 is in a still darker portion of image 64 than is location pointer 72,as indicated by location pointer 78 on lightness/darkness scale 66 inFIG. 13B, wherein a greater amount of reduction of usage of diluted inkoccurs than at the portion of image 64 indicated by location pointer 72.

It will also be appreciated by those skilled in the art that based onthe above method steps, the reduction in usage of the diluted ink isgreater in magnitude than the increase in usage of the saturated ink,such that a total usage of the diluted ink and the saturated ink asexpressed in the final colorant space is less than a total usage of thediluted ink and the saturated ink as expressed in the initial colorantspace. Thus, less ink overall is ejected onto substrate 44, reducing thelikelihood of paper cockling, soak-thru, mottling, and smearing.

Although both FIGS. 13A and 13B are in the form of grayscale images, itwill be appreciated by those skilled in the art that FIGS. 13A and 13Bare used for illustrative purposes, and that the present descriptionapplies equally to color images, for example, 8-bit color images,wherein the digital count for each level/color varies on a scale of 0 to255.

Referring now to FIG. 14, the generation of color conversion lookuptable 62 based on the final colorant space, as set forth in step S106 ofFIG. 3, is described in greater detail below with respect to stepsS106-1 to S106-11.

Any calibration and color table building procedures for the 3-color(CMY) printing can be easily applied to the final colorant space. In thepresent embodiment, the three variables (x₀, x₁, x₂) are treated asthree nominal inks which are analogues to (C, M, Y) variables of 3-colorprinting. The difference is that each combination of the C, M, and Yvariables contains only three inks (C,M,Y), whereas each combination ofthe x₀, x₁, and x₂ variables contains six inks (C,M,Y,K,c,m). Aprocedure for generating color conversion lookup table 62 is accordinglydescribed below.

At step S106-1, N (e.g., N=9) evenly-spaced points are selected for eachof the three variables (x₀, x₁, x₂), forming a total of N³ (e.g.,9³=729) combinations. Each combination of the x₀, x₁, and x₂ variableswill contain six inks (C,M,Y,K,c,m) in the final colorant space.

At step S106-3, N³ color patches are printed using the N³ combinationpoints.

At step S106-5, the L*, a*, b* values for each color patch are measured,for example, using a spectrophotometer. This provides a data setcorrelating the N³ colorant points (x₀, x₁, x₂) with a corresponding N³points (L*, a*, b*) in device-independent color space. Using athree-dimensional interpolation method with respect to (x₀, x₁, x₂), theL*, a*, b* values can be computed for each color mixing point of thefinal colorant space. Each mixing point (x₀, x₁, x₂) is associated withthe pre-determined six inks, and the relationship between (C,M,Y,K,c,m)and (L*, a*, b*) is established, which is called a printer profile.

At step S106-7, a target profile is determined. If the main applicationof imaging apparatus 12 is to reproduce the monitor-displayed images,the monitor profile is selected as the target profile. In the targetprofile, the relationship between monitor (R,G,B) (Red, Green, and Bluecolors) and (L*,a*,b*) is established.

At step S106-9, gamut mapping is performed. Since the color ranges thatcan be produced are different between the monitor and imaging apparatus12, mapping the color ranges between the two devices is necessary, andmay be performed using techniques known in the art.

At step S106-11, color conversion lookup table 62 is built based on theresults of the gamut mapping between the monitor and the final colorantspace of imaging apparatus 12. The transformation from one colorantspace to another colorant space is usually performed using a colortable, such as color conversion lookup table 62. For color reproductionfrom monitor input values to imaging apparatus 12 CMYKcm color values,the input to color conversion lookup table 62 is (R, G, B) and theoutput of color conversion lookup table 62 is (C,M,Y,K,c,m). In buildingthe color conversion lookup table 62, Q (e.g., Q=17) even-spaced pointsfor each of the R, G, and B colors are selected, giving a total of Q³(e.g., 17³=4913) combinations. The color values (L*, a*, b*) for eachcombination are then found from the monitor profile. Inverting theprinter profile and using the color values as input will give thecorresponding printer colorant values (C,M,Y,K,c,m). When imagingapparatus 12 and/or imaging driver 58 receives R, G, and B color valuesfor an image, it will lookup (or interpolate) the corresponding C, M, Y,K, c, m values in color conversion lookup table 62 for reproducing theimage.

While this invention has been described with respect to exemplaryembodiments, it will be recognized that the present invention may befurther modified within the spirit and scope of this disclosure. Thisapplication is therefore intended to cover any variations, uses, oradaptations of the invention using its general principles. Further, thisapplication is intended to cover such departures from the presentdisclosure as come within known or customary practice in the art towhich this invention pertains and which fall within the limits of theappended claims.

1. A method of selecting inks for use in imaging with an imagingapparatus, said method comprising: determining a maximum usage of adiluted ink for use in conjunction with a saturated ink based on visualperception characteristics relating to a combination of said diluted inkand said saturated ink; generating an initial colorant space based onsaid maximum usage of said diluted ink, said initial colorant spaceexpressing an initial usage of said diluted ink and an initial usage ofsaid saturated ink at each point in said initial colorant space;optimizing said initial usage of said diluted ink and said initial usageof said saturated ink in said initial colorant space to generate a finalusage of said diluted ink and a final usage of said saturated ink in afinal colorant space; and generating a color conversion lookup tablebased on said final colorant space.
 2. The method of claim 1, furthercomprising: printing a plurality of color patches on a substrate usingsaid diluted ink and said saturated ink; and determining at least one ofgranularity, gloss, and a substrate ink tolerance, based on saidplurality of color patches, wherein said visual perceptioncharacteristics are determined based on said at least one of saidgranularity, said gloss, and said substrate ink tolerance.
 3. The methodof claim 2, wherein: said determining said at least one of saidgranularity, said gloss, and said substrate ink tolerance is determiningat least two of said granularity, said gloss, and said substrate inktolerance; and said determining said maximum usage of said diluted inkis selecting a lowest maximum usage of said diluted ink as individuallydetermined based on each of said at least two of said granularity, saidgloss, and said substrate ink tolerance.
 4. The method of claim 1,further comprising generating mixing tables to determine both saidinitial usage of said diluted ink and said initial usage of saidsaturated ink based on said maximum usage of said diluted ink, whereinsaid initial colorant space is generated based on said initial usage ofsaid diluted ink and said initial usage of said saturated ink.
 5. Themethod of claim 1, wherein said optimizing said initial usage of saiddiluted ink and said initial usage of said saturated ink in said initialcolorant space yields a reduction in usage of said diluted ink and anincrease in usage of said saturated ink in said final colorant space ascompared to said initial colorant space.
 6. The method of claim 5,wherein said reduction in usage of said diluted ink and said increase inusage of said saturated ink occurs exclusively at darker portions of animage printed by said imaging apparatus using said color conversionlookup table.
 7. The method of claim 5, wherein an amount of saidreduction in usage of said diluted ink increases with increasingdarkness within an image printed by said imaging apparatus using saidcolor conversion lookup table, and an amount of said increase in usageof said saturated ink increases with said increasing darkness.
 8. Themethod of claim 5, wherein said reduction in usage of said diluted inkis greater in magnitude than said increase in usage of said saturatedink such that a total usage of said diluted ink and said saturated inkas expressed in said final colorant space is less than a total usage ofsaid diluted ink and said saturated ink as expressed in said initialcolorant space.
 9. The method of claim 1, wherein said diluted ink isone of a pigment-based ink and a dye-based ink, and wherein saidsaturated ink is the other of said pigment-based ink and said dye-basedink.
 10. A method of selecting inks for use in imaging with an imagingapparatus, said method comprising: printing a plurality of color patcheson a substrate using a diluted ink and a saturated ink; determining atleast two of granularity, gloss, and a substrate ink tolerance, based onsaid plurality of color patches; determining a maximum usage of saiddiluted ink for use in conjunction with said saturated ink based onvisual perception characteristics relating to a combination of saiddiluted ink and said saturated ink, wherein said visual perceptioncharacteristics are based on said at least two of said granularity, saidgloss, and said substrate ink tolerance; generating an initial colorantspace based on said maximum usage of said diluted ink, said initialcolorant space expressing an initial usage of said diluted ink and aninitial usage of said saturated ink at each point in said initialcolorant space; and generating a color conversion lookup table based inpart on said initial colorant space.
 11. The method of claim 10, whereinsaid determining said maximum usage of said diluted ink is selecting alowest maximum usage of said diluted ink as individually determinedbased on each of said at least two of said granularity, said gloss, andsaid substrate ink tolerance;
 12. The method of claim 10, furthercomprising: generating mixing tables to determine both said initialusage of said diluted ink and said initial usage of said saturated inkbased on said maximum usage of said diluted ink, wherein said initialcolorant space is generated based on said initial usage of said dilutedink and said initial usage of said saturated ink.
 13. The method ofclaim 10, wherein said diluted ink is one of a pigment-based ink and adye-based ink, and wherein said saturated ink is the other of saidpigment-based ink and said dye-based ink.
 14. A method of selecting inksfor use in imaging with an imaging apparatus, said method comprising:generating an initial colorant space, said initial colorant spaceexpressing an initial usage of said diluted ink and an initial usage ofsaid saturated ink at each point in said initial colorant space;optimizing said initial usage of said diluted ink and said initial usageof said saturated ink in said initial colorant space to generate a finalusage of said diluted ink and a final usage of said saturated ink in afinal colorant space; and generating a color conversion lookup tablebased on said final colorant space.
 15. The method of claim 14, whereinsaid optimizing said initial usage of said diluted ink and said initialusage of said saturated ink in said initial colorant space yields areduction in usage of said diluted ink and an increase in usage of saidsaturated ink in said final colorant space as compared to said initialcolorant space.
 16. The method of claim 15, wherein said reduction inusage of said diluted ink and said increase in usage of said saturatedink occurs exclusively at darker portions of an image printed by saidimaging apparatus using said color conversion lookup table.
 17. Themethod of claim 15, wherein an amount of said reduction in usage of saiddiluted ink increases with increasing darkness within an image printedby said imaging apparatus using said color conversion lookup table, andan amount of said increase in usage of said saturated ink increases withsaid increasing image darkness.
 18. The method of claim 15, wherein saidreduction in usage of said diluted ink is greater in magnitude than saidincrease in usage of said saturated ink such that a total usage of saiddiluted ink and said saturated ink as expressed in said final colorantspace is less than a total usage of said diluted ink and said saturatedink as expressed in said initial colorant space.
 19. The method of claim14, wherein said diluted ink is one of a pigment-based ink and adye-based ink, and wherein said saturated ink is the other of saidpigment-based ink and said dye-based ink.